Gamma ray beams for - PowerPoint Presentation

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Gamma

ray beams for Nuclear Astrophysics: first results of tests and simulations of the ELISSA array

Marco La Cognata

The 3rd ELIMED Workshop 7-10 September 2016 Laboratori Nazionali del Sud of INFN

- High

power laser system, 2 x 10PW maximum power- Gamma radiation beam, high intensity, tunable energy up to 20MeV, relative bandwidth 5 10-3, produced by Compton scattering of a laser beam on a 700 MeV

electron beam produced by a warm LINAC

Magurele

, RomaniaPhoton scattering on ultra relativistic electrons

Nuclear

Astrophysics @ ELI-NPNuclear physics with high power lasers:Fission & FusionProduction of exotic nucleiNuclear

reactions in plasmas & electron screeningNuclear excitations in plasma

…Photo dissociation reactions

Nuclear spectroscopy and cluster studiesPhotofission Investigation of GDR and Pigmy Dipole ResonanceNuclear astrophysicsDirect measurements: reactions in explosive environmentsIndirect measurements: investigation of radiative

capture

reactions

Industrial &

medical

applications

,

material

science…

Nuclear

Astrophysics @ ELI-NPFor the first time high intensity (>107 γ/s) high resolution (5 10-3) will be available, making it possible to measure photodissociation reactions of astrophysics importance. A few physical cases to be addressed @ ELI-NPHe-burning in stars

12C(α,γ)16O through the 16O(γ,α)12C reaction

[indirect measurement]3α12

C+γ through the 12C(γ,3α) reaction [indirect measurement]Si-burning in stars and presupernova phase- 24Mg(γ,α)20Ne

Nuclear

Astrophysics @ ELI-NPFor the first time high intensity (>107 γ/s) high resolution (5 10-3) will be available, making it possible to measure photodissociation reactions of astrophysics importance. A few physical cases to be addressed @ ELI-NPHe-burning in stars

12C(α,γ)16O through the 16O(γ,α)12C reaction

[indirect measurement]3α12

C+γ through the 12C(γ,3α) reaction [indirect measurement]Si-burning in stars and presupernova phase- 24Mg(γ,α)20Ne p-process (production of proton rich nuclei along the stability valley)96Ru(γ,α)92Mo74Se(γ,p)73As Indirect measurements: the detailed balance principle is used to deduce the cross section of interest from the one of the time-reversed process.

NA

experiments with gamma beams A SSD array is very flexible as it can be used to measure photodissociation on many nuclei, including noble gases (using a gas cell) and long lived unstable nuclei (such as 7Be, 14C or 26Al)For nuclear astrophysics, typical gamma energies are right above the particle emission thresholds

Gamma energies around 10 MeV are typically necessary

Particles are emitted with energies ranging from hundreds keV up to few MeV

Consequences on the design of a SSD array:Large area coverage is necessary as beam intensity & cross section are relatively lowDetector granularity is not an issue as two or three particles at most are emitted per reaction eventLow threshold detectors are necessary, to keep detection efficiency as large as possibleNo PSD or DE techniques are viable for particle ID

The ELI-NP SSD array

Requirements:Low detection thresholdLow energy particles (< few MeV)  no ΔE detector,

ToF, PSDHigh energy and angular resolution for

kinematic particle ID

24Mg(γ,α)20NeTypical cross section to be measured~3 104 events per day expected at 11 MeV

Silicon burning is analogous to

neon burning in that it proceeds by photodisintegration and rearrangement, but it involves many more nuclei and is quite complex.The reaction 28Si + 28Si  (56Ni)* does not occur owing to the large Coulomb inhibition. Rather a portion of the silicon (and sulfur, argon, etc.) “melt” by photodisintegration reactions into a sea of neutrons, protons, and alpha-particles. These lighter constituents add onto the remaining silicon and heavier elements, gradually increasing the mean atomic weight until species in the iron group are most abundant.The

nucleosynthesis is governed by the slowest reaction in the network:24Mg(g,

a)20

NeIts cross section is affected by a factor of 2uncertainty.Equilibrium  synthesis of the most tightly bound nuclei  formation of an “iron” core pre-supernova conditionsA physical case

Drawings

of the detectorThe SSD array covers about

80% of 4π Thanks to the use of charge-partition position sensitive detectors the number of electronic channel

is ~300

Simulated

spectraParticle yield for a 11 MeV gamma beam impinging on a 24Mg target with C backingEnergy and angular resolution of detectors, gamma beam energy spread and emittance, straggling into dead layers were accounted forSignal is much stronger than background (3 orders of magnitude)

Kinematic separation viable

Background (GEANT4)

Neutron background includes: Neutrons emitted in photodissociation

reactions off target nuclei (see picture on the left)Neutrons emitted in reaction triggered by scattered photons (negligible)

Electromagnetic background includes: Electrons and gammas from Compton scattering

Electron-positron pairsPhotons from nuclear or atomic deexcitation The picture on the right shows the gamma per second hitting the whole detector  negligible rate & damage

Prototype @ LNS

The ELI-NP detectors

#35 X3 position sensitive detectors in barrel configuration Energy resolution (FWHM) ~ 0.3%

Angular resolution 1 mm or ~ 0.4 deg

8 QQQ3 DSSSD as end cap detectorsEnergy resolution (FWHM) ~ 0.3%Angular resolution 3 mm or ~ 0.8 deg

Standard

electronics & GET16 - fold preamplifier +

shaper with timing filter and discriminators, multiplexed output Since

low energy gamma

rays are used, max 3 particles per event are emitted Multiplexing well suited!Above: GET belonging to ASFIN collaboration for a future DACQ for nuclear physics experiments with SSDIn collaboration with the CHIMERAGroup @ LNS we are implementing GET for nuclear astrophysics

Tests @ LNS

Design goal:- Low threshold (few hundredes keV)- Angular resolution better than 1 cm- Energy resolution better than 1%Experiments:- alpha sources - a 11 MeV

7Li beam from the INFN-LNS tandem was delivered onto on Au (about 100 µg/cm2) and 12C (about 60 µg/cm2) targetsGrids with equally spaced slits of different sizes were used to estimate position resolution

Experimental spectra

To measure the detection threshold, we have performed a run using a standard 3-peak alpha source and a americium source shielded by a 17 µm thick Al foil. This degrader shift the energy peak to 1 MeV and, due to energy straggling, the energy range spanned reached zero.

 300

keV

threshold achieved owing to a hot collimator close to detectors. Lower threshold achieved in other chambers.Position resolution at high energies (11 MeV, left panel) and low energies (1 MeV, right panel).  Resolution better than 1 mm at high energies and about 6 mm at low energies

Conclusions

- The advent high-intensity & high resolution gamma-ray beam facilities is a great opportunity for nuclear physics and astrophysics, as a number of reaction of key astrophysical importance can be measured for the first time- ELI-NP cutting-edge features must couple with high-performance detectors- For nuclear astrophysics, particles of energies as low as few hundreds keV are emitted, making it necessary a careful detector implementation- GEANT4 simulations have been performed, implementing the detector configurations are updating the physics wherever necessary (especially in the case of photodissociation reactions)

- A SSD array in barrel configuration (plus end cap detectors) turns out to be a very suited tool for nuclear astrophysics studiesTHANKS FOR YOUR ATTENTION

Collaboration

M. La Cognata, A. Anzalone, V. Crucillà, G.L. Guardo, M. Gulino, D. Lattuada, R.G. Pizzone, S. Romano, C. Spitaleri, A. Taffara, A. Tumino

C. Matei, D. Balabanski, S. Chesnevskaya, D. M. Filipescu

, O. Tesileanu, Yi Xu